Where do I put my mocks?

Question

I'm struggling to get mocks working, for a change, and was wondering where people generally put their mock classes. I seem to have three basic choices none of which seem to work.

I can put them in with the application assembly itself, in which case they ship with the application, which seems bad, but they are available for unit tests during the final builds and there are no circular references. This seems the simplest approach.

I can create a separate mock assembly, so they are available during the unit tests, can be consumed from the application and the test application but I end up with either having to move all of the actual types to this assembly or creating circular references.

I can put them in the test assembly, but then they are unable to be used from the application itself and therefore I cant use them as a process for building up chunks of the application.

I tend to try and use the mocks for helping develop the system as well as for the testing parts and therefore I find it hard to know where to put them. Additionally all of the final releases of code have to run through unit test processes therefore I need the mocks available during the build cycle.

Does anyone have any thoughts as to where mock classes should be placed?

thanks for any help T

Answer 1

Your mocks should go in your unit tests projects. Your application should not be dependent on your mock objects. Generally your application will use interfaces and your mocks will implement those interfaces. Your application won't need to or should reference your test project.

Answer 2

Mocks should be kept in a separate project. We have a total of 3 options

1. Mocks in a unit test project

   Will not work if the UI project needs to use this for startup(eg:mock service/partial integration test/smoke test). Even if the test project is referenced in config file through dependency injection, we do not want to carry unit test dlls to other environments. More over focus is more on integration tests these days as Unit tests are less productive, which of course is outside of this topic but we should realise mocks are not just about unit tests.

2. Mocks in the application projects itself(service-mocks in service-project)

   Developers can accidentally forget to remove the mocks. eg: a new developer tries mocks and forgets to include it in dependency config files. Let us not leave it for chances as it can hinder expansion of teams.

3. Mocks in a separate project.

   Here both unit test projects, as well as other startup projects, can refer this. Integration tests using front end has the additional possibility to mock a certain area(eg: external APIs). Or smoke test the UI with mocks(while other teams deploy the back end). In short, we have a lot of options to use the mock. Not tied to unit test alone. But the most important benefit is, when we want to be sure of going live, we can remove mock project(or dll) from deployment. This way if any project or config files accidentally refer the mock, we get runtime error. Which helps to nip it in the bud.